Method and apparatus for developing resist

ABSTRACT

A resist developing apparatus has a plurality of developing solution containers each provided with a temperature regulator, a mixture tank connected to the plurality of developing solution containers, a flow control valve connected between the mixture tank and each developing solution container, a temperature detector for detecting the temperature of developing solution in the mixture tank, and a control system for controlling the flow control valve in accordance with the temperature detected by the temperature detector. As the development progresses, the temperature of the developing solution is lowered to stop the development. Thereafter, the developing solution is supplanted by rinsing solution.

This application is a continuation of application Ser. No. 08/110,931,filed Aug. 24, 1993, now abandoned.

BACKGROUND OF THE INVENTION

a) Field of the Invention

The present invention relates to a technique for developing resist athigh precision.

b) Description of the Related Art

Forming a resist pattern at high precision has long been desired assemiconductor integrated circuits have become highly integrated. In thisspecification, a term "resist" collectively means any resist sensitiveto energy beams, such as photoresist and electron beam (EB) resist.

Positive type resist and negative type resist Bare known. Of thepositive type resist, the region where an energy beam such as a lightbeam and electron beam was applied is removed. Of the negative typeresist, the region where an energy beam was riot applied is removed.

EB resist of high resolution will be explained illustratively. Generallyused as EB resist are styrene based or methacrylic acid based positiveresist, and styrene based negative resist. EB resist is generally coatedby a spinner on the surface of an underlie such as a reticle quartzsubstrate and a Si substrate, and exposed by an electron beam.

An EB resist film after being exposed undergoes a development process.This development process generally includes:

(1) development process,

(2) a rinse process, and

(3) a dry process.

In the development process, an EB resist film is selectively dissolvedby organic solvent by a chemical property difference between the exposedregion and unexposed region off the EB resist film. Developing solutionnot only selectively dissolves the exposed region or unexposed region,but also swells the unremoved EB resist film.

In the rinse process, the developing solution is supplanted by rinsingsolution. The rinse process has a function of tightening and condensingthe resist film swelled by the developing solution as well as thefunction of stopping the development. As the rinsing solution for EBresist, organic solvent having a lower resist solubility than developingsolution is generally used.

For example, for positive type EB resist, there are used a mixedsolution of methylethylketone and methylisobutylketone as the developingsolution and a mixed solution of isopropylalcohol andmethylisobutylketone as the rinsing solution. For negative type EBresist, there are used a mixed solution of isoamylacetate and ethyleneglycol monoethyl ether as the developing solution and ethylene glycolmonoethyl ether as the rinsing solution.

After the development is stopped and the original condensed state of theswelled resist film is recovered, the resist film is dried to completethe developing program.

A new defect has been found recently during a resist developmentprocess. Namely, precipitate as thick as 1 μm is left in a hole formedby the development process. This phenomenon Is conspicuous particularlyin the case of positive type resist. The cause of generating such adefect may be reasoned from the following.

In the developing process, resist is dissolved into developing solution.Developing solution has a high solubility relative to resist. Positivetype EB resist after the development process reduces its thickness, andthe ratio of a finished film thickness to the original film thickness isonly about 90%. The solubility of negative type EB resist intodeveloping solution is lower than that of positive type EB resist.However, the ratio is in the order not negligible.

During the transition period from the development process to the rinseprocess, the developing solution and rinsing solution contact each otherand are mixed together. Part of the resist components dissolved greatlyin the developing solution is immersed in the rinsing solution and isdeposited as precipitate again on the surface of the underlie, becauseof a low solubility of the rinsing solution.

For example, if precipitate having a diameter of about 1 μm is depositedin a window formed in a reticle, a defect of about 0.2 μm is formed on asubject exposed at a reduction ratio of 1/5. This defect of about 0.2 μmis fatal to a highly integrated semiconductor device.

Such a defect is formed not only on negative type resist but also onpositive type resist, and not only on EB resist but also on photoresist.

A defect caused by resist re-deposition is formed due to a solubilitydifference between developing solution and rinsing solution. In order torelieve an abrupt change in the solubility, it is conceivable that aplurality of rinsing solutions or a plurality of mixed solutions ofdeveloping and rinsing solutions at different compositions are preparedto transit form the developing process to the rinsing process whilegradually changing the resist solubility.

As described above, a surface defect by resist re-deposition on thereticle surface is caused by a solubility difference between developingand rinsing solutions.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel resistdeveloping technique.

It is another object of the present invention to provide a resistdeveloping technique capable of preventing dissolved resist from beingre-deposited on the surface of an underlie.

According to one aspect of the present invention, there is provided aresist developing apparatus having a plurality of developing solutioncontainers each provided with a temperature regulator, a mixture tankconnected to the plurality of developing solution containers, a flowcontrol valve connected between the mixture tank and each developingsolution container, a temperature detector for detecting the temperatureof developing solution in the mixture tank, and a control system forcontrolling the flow control valve in accordance with the temperaturedetected by the temperature detector.

According to another aspect of the present invention, there is provideda resist developing method including the steps of preparing developingsolutions having different temperatures in different containers, mixingthe developing solutions having different temperatures to make mixeddeveloping solution having a predetermined temperature, and developingresist by using the mixed developing solution having the predeterminedtemperature.

Developing solutions are contained in a plurality of developing solutioncontainers and set to different temperatures. The developing solutionshaving different temperatures are mixed together in the mixture tank toobtain developing solution having a predetermined temperature. Bychanging the temperature during the development process, various typesof development processes are possible.

For example, if developing solution at a low temperature is used, theresist profile can be improved. If developing solution at a hightemperature is used, the time required for the development process canbe shortened.

The development is performed at predetermined speeds using developingsolution whose temperature is changed with time. As the temperature ofthe developing solution is gradually lowered, the resist solubility ofthe developing solution gradually lowers. When the resist solubility ofthe developing solution becomes sufficiently low, the development issubstantially stopped.

With such a temperature change, it is possible to stop the developmentwithout supplanting the developing solution by rinsing solution. Afterthe resist solubility of the developing solution becomes sufficientlylow, the developing solution is supplanted by rinsing solution so thatresist dissolved in the developing solution can be prevented fromre-deposition.

The development is stopped not by supplanting the developing solution bythe rinsing solution, but by the temperature change of the developmentsolution. The function of tightening the swelled resist film is providedby the rinsing solution as conventional.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a resist developing apparatusaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 showing a resist developing apparatus according toan embodiment of the invention, canister tanks 1a and 1b contain thesame kind of developing solutions, such as a mixed solution ofisoamylacetate and ethylene glycol monoethyl ether.

Pipes are connected between the canister tanks and constant temperaturebaths 2a and 2b whereat the temperatures of the solutions are maintainedconstant. The solutions are introduced via control valves 3a and 3b intoa mixture tank 4 wherein the solutions are mixed together. Each constanttemperature bath 2 can be set to a desired temperature, for example,within a range from about 10° to 25° C. For example, the constanttemperature bath 2a is set to 10° C., and the constant temperature bath2b is set to 25° C.

The mixture ratio of developing solutions in the mixture tank 4 can becontrolled by the control valves 3a and 3b. The developing solution tobe supplied from the mixture tank 4 can be set to a desired temperaturewithin a range from about 10° to 25° C. for example.

Other lines are also connected to the mixture tank 4. For example, aline including a canister tank 1n, constant temperature bath 2n, andcontrol valve 3n is connected to the mixture tank 4. These lines areused for supplying the same kind of developing solutions at differenttemperatures or different kinds of developing solutions. A purge linemay be installed. A control valve may be provided downstream of themixture tank 4.

An output line of the mixture tank 4 is connected via a filter 5 to aspray tip 21. A tap nozzle may be used in place of the spray tip.Another line including a canister tank 11 containing rinsing solution,constant temperature bath 12, control valve 13, and filter 15, is alsoconnected to the spray tip 21. Another pipe line and another spray tipor tap nozzle may be used solely for the rinsing solution.

A temperature detector 17 is set to the mixture tank 4 to measure thetemperature of the developing solution in the tank 4 in a contact ornon-contact manner. The detected temperature in the form of electricalsignal is supplied to a controller 18 which generates signals forcontrolling the control valves 3.

Specifically, in the above example, if the temperature of the developingsolution to be supplied at a temperature T rises, the controller 18controls the low temperature side control valve 3a toward the opendirection and the high temperature side control valve 3b toward theclose direction.

A spinner 25 is placed under the spray tip 21. The spinner 25 has aplate 27 coupled to the drive shaft of a motor 26 and a cup 29surrounding the plate 27.

In the above description, two kinds of developing solutions at differenttemperatures and of the same component are used. Three or more kinds ofdeveloping solutions at different temperatures may be used. Theprecision of temperature control can be improved if the temperatures atboth the constant temperature baths 2a and 2b are set so that thetemperature of the developing solution in the mixture tank 4 changesless with a change in the mixture ratio. Developing solutions ofdifferent compositions may be used if the solubilities relative toresist are not so different.

With the developing apparatus described above, the developing processcan be performed using developing solution set to a predeterminedtemperature. For example, the developing solution is set to a lowtemperature and the development process is executed slowly to obtain ahigh precision profile, or the developing solution is set to a hightemperature to execute the development process at high speed.

The controller 18 may include a timer, memory, comparator, and the liketo represent the temperature profile of the development process as thefunction of time to make the development process have a temperaturechange with time. For example, most of the development process iscarried out at a predetermined constant temperature, and thereafter thetemperature of the developing solution is gradually loweredproportionally with the lapse of time measured by the timer until thedevelopment is stopped by the lowered temperature of the developingsolution.

The temperature detector 17 measures the temperature of the developingsolution in the mixture tank 4. The controller 18 compares the measuredtemperature with the setting temperature, and if both the temperaturesare different, regulates the control valve 3 to change the mixture ratioand make both the temperatures become the same.

A plurality of lines for supplying developing solutions of the samecomposition kept at successively decreasing temperature may be used sothat the temperature of the final developing solution can be graduallyand stepwisely changed at the final stage of the developing process.

After the development ceases at the lowered temperature of thedeveloping solution sprayed from the spray tip 21, time supply of thedeveloping solution is stopped and the rinsing solution in the canistertank 11 is supplied to the same spray tip 21. The supply of the rinsingsolution supplants time developing solution, and tighten the swelledresist to recover the original condition.

Valves may be provided upstream of the junction of the developingsolution supply line and rinsing solution supply line. The spray chipmay be replaced by a tap nozzle.

In the above description, the temperature of the developing solution isset to an optional value within the range from 10° to 25° C. Thetemperature range is not limited to this range. If the temperature ofthe developing solution is required to be set to near that of a cleanroom which is generally controlled at a temperature of 22° C., it ispreferable to set the temperature of developing solution, if usingorganic solvent, to about 25° C. because the solution temperature islowered by its heat of vaporization.

Developing solution higher than 25° C. may also be used to develop athigh speed. If developing solution unable to stop the development at 10°C. is to be used, the temperature range is extended further to the lowertemperature side.

In addition to a rinsing solution line, a pure water line and the likemay be added to the apparatus.

In the above description, the temperature of the developing solution inthe mixture tank 4 is detected and the controller 18 controls themixture ratio of the developing solution to have a predeterminedtemperature. Instead, the resist under the development may be monitoredso that the monitor output signal is supplied to the controller 18 tocontrol the development process.

In developing resist at high resolution, the temperature of thedeveloping solution is gradually lowered until the development isstopped. In this manner, resist once dissolved in the developingsolution can be prevented from being re-deposited on the reticlesurface. Accordingly, it is possible to eliminate defective reticles tobe caused by resist re-deposition and to manufacture reticles of highprecision at high yield.

The present invention has been described in connection with the aboveembodiments. The invention is not intended to be limited only to theembodiments, but it is apparent for those skilled in the art thatvarious substitutions, changes, improvements, combinations, and the likeare possible.

We claim:
 1. A resist developing method for developing a resist filmsensitive to an energy beam and which has been selectively exposed tothe energy beam so that the resist film has exposed and unexposedregions, said method comprising the steps of:preparing developingsolutions having different temperatures in different containers, eithersaid exposed regions of the resist film or alternatively said unexposedregions of the resist film having a solubility in the developingsolutions which is reduced as the temperature of the developing solutionis lowered; mixing said developing solutions having differenttemperatures at a mixture ratio to provide a mixed developing solutionhaving a predetermined temperature; subsequent to said mixing step,applying said mixed developing solution having said predeterminedtemperature to the resist film to thereby remove either the exposedregions of the resist film or the unexposed regions of the resist film;further mixing said developing solutions having different temperatures,while changing the mixture ratio of said developing solutions as thedevelopment proceeds to thereby gradually lower the temperature of themixed developing solution; and further applying said mixed developingsolution having the gradually lowered temperature to said resist film.2. A resist developing method according to claim 1, further comprisingthe step of measuring the temperature of said mixed developing solutionduring said step of mixing the developing solutions, and if saidmeasured temperature is different from said predetermined temperature,changing the mixture ratio of said mixed developing solution so as tobring the temperature of the mixed developing solution to saidpredetermined temperature.
 3. A resist developing method according toclaim 2, wherein said temperature of the mixed developing solutionduring said mixing step and during said further mixing step is within arange from about 25° C. to about 10° C.
 4. A resist developing methodfor developing a resist film sensitive to an energy beam and which hasbeen selectively exposed to the energy beam so that the resist film hasexposed and unexposed regions, said method comprising the stepsof:preparing first and second developing solutions having differenttemperatures in different containers, either said exposed regions of theresist film or alternatively said unexposed regions of the resist filmhaving a solubility in the developing solutions which is reduced as thetemperature of the developing solution is lowered; mixing said first andsecond developing solutions having different temperatures at a mixtureratio to provide a mixed developing solution; subsequent to said mixingstep, applying said mixed developing solution to the resist film tothereby remove either the exposed regions of the resist film or theunexposed regions of the resist film and thereby develop the resistfilm; holding said mixture ratio of said developing solutions constantduring a first developing period to thereby maintain said mixeddeveloping solution at a constant temperature during said firstdeveloping period; and thereafter continually changing the mixture ratioof said developing solutions having different temperatures during asecond developing period in such a manner that the temperature of themixed developing solution is gradually lowered during said seconddeveloping period.
 5. A resist developing method according to claim 4,wherein said temperature of the mixed developing solution is loweredstepwise during said second period.
 6. A resist developing methodaccording to claim 4, wherein the mixture ratio of said first and seconddeveloping solutions is continually changed during said second period tothereby gradually lower the temperature of the mixed developmentsolution until such time as the development of the resist isdiscontinued.